A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
1. What is the difference between working stress approach and limit
state approach? (GI1)
For working stress approach, service loads are used in the whole design
and the strength of material is not utilized in the full extent. In this method
of design, stresses acting on structural members are calculated based on
elastic method and they are designed not to exceed certain allowable
values. In fact, the whole structure during the lifespan may only experience
loading stresses far below the ultimate state and that is the reason why this
method is called working stress approach. Under such scenario, the most
economical design can hardly be obtained by using working stress
approach which is now commonly used in the design of temporary works.
For limit state approach, for each material and load, a partial safety factor
is assigned individually depending on the material properties and load
properties. Therefore, each element of load and material properties is
accurately assessed resulting in a more refined and accurate analysis of
the structure. In this connection, the material strength can be utilized to its
maximum value during its lifespan and loads can be assessed with
reasonable probability of occurrence. Limit state approach is commonly
used for the majority of reinforced concrete design because it ensures the
utilization of material strength with the lowest construction cost input.
2. What are the functions of different components of paint? (GI2)
For normal paint application, there are mainly three main components of
paint, namely primer, undercoat and finishing coat.
Primer: This is the first layer of a typical painting system and it is used to
inhabit corrosion and provide a good bond for subsequent coats.
Undercoat: This component acts as a barrier to corrosion agents and even
out irregularities of bonding surface. It also serves to hide the underlying
background and prevent the details and colour of the area of application to
affect the designed colour and finishing details of paint.
Finishing coat: This is the final layer of a typical painting system and it
protects the underlying layers from the effect of adverse weather conditions
(e.g. sunlight) and to provide the designed properties of paint like colour,
impermeability, wearing resistance, etc.
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